Fertiliser Factory

Feeding the crops

Plants need three main nutrients from the soil, and fertilisers replace them so crops keep growing well. The three are nitrogen, phosphorus and potassium, and a fertiliser that supplies all three is called an NPK fertiliser. Each has its own job. Nitrogen drives leafy green growth above the ground. Phosphorus builds healthy roots. Potassium helps flowers and fruit form and helps the plant resist disease. These nutrients are made into fertilisers in factories. Nitrogen fertilisers are ammonium salts, made by reacting ammonia with an acid. Phosphorus comes from phosphate rock treated with acid, and potassium comes from potassium salts dug from the ground by mining. This module covers the nutrients and how they are produced.

Fertiliser words

Learn these before you match any nutrient, and keep each plant-growth role in mind.

Making the fertilisers

Different nutrients are produced in different ways, so it helps to set the nitrogen route beside the phosphate route.

How to match a nutrient to a need

Do not just recite the three letters. Read the plant and pick the nutrient that fixes it. Weak, pale leaves point to nitrogen, since it feeds the leafy growth above ground. Poor roots point to phosphorus. Few flowers or fruit, or a plant that keeps falling ill, point to potassium. Name the nutrient, say what it does, and match it to the exact problem in front of you rather than listing all three.

Match the nutrient to its job

Which nutrient is needed?

A crop has weak, pale leaves and very little green growth above the soil. Which nutrient does it most likely need?

• Nitrogen.
• Phosphorus.
• Potassium.
• Extra oxygen in the soil.

How fertilisers are made

Select the TWO correct statements about making fertilisers.

• Ammonium salts are made by reacting ammonia with an acid
• Potassium salts are obtained by mining
• Fertilisers are made from nothing but thin air
• Fertilisers are made by burning plastic

Total NPK parts

An NPK fertiliser is labelled 20-10-10, meaning 20 parts nitrogen, 10 parts phosphorus and 10 parts potassium. Add the three numbers to find the total parts of nutrient.

Order making a nitrogen fertiliser

Put the stages of making a nitrogen fertiliser in order, earliest first.

• Ammonia is supplied as the starting material
• The ammonia is reacted with an acid such as nitric acid
• An ammonium salt forms, such as ammonium nitrate
• The salt is dried and bagged as fertiliser

Complete the facts

The nutrient that drives leafy green growth is _____. The nutrient that builds healthy roots is _____. The nutrient that helps flowers, fruit and disease resistance is _____. A nitrogen fertiliser made from ammonia and an acid is an _____ salt.

Match the source to the nutrient it gives

Spot the true fertiliser facts

Tap the TWO statements that are true about NPK fertilisers.

• Nitrogen helps leafy green growth
• Ammonium salts are made from ammonia and an acid
• Potassium is what builds a plant roots
• Plants need no nutrients from the soil at all

Choose the nutrient

Read each case and choose the best nutrient, with a reason.

• A gardener has plants with strong leaves but very few flowers and fruit. Which nutrient should the fertiliser be rich in?
• A factory wants to make a nitrogen fertiliser. What should it react the ammonia with?
• A student writes only that a plant needs NPK, with no roles given. How could the answer be improved?

Explain NPK fertilisers

A farmer buys an NPK fertiliser for a struggling crop. Explain what the three nutrients do and how such fertilisers are made.

• Name the three nutrients in an NPK fertiliser
• Give the plant-growth role of nitrogen and of potassium
• Explain how a nitrogen fertiliser is made from ammonia
• Explain where phosphorus and potassium come from
• Finish with a judgement on which nutrient a poorly rooted plant needs and why